Читать книгу Chemical Analysis - Francis Rouessac - Страница 75

The gas chromatograph comprises a temperature‐controlled enclosure, or ventilated oven, in which the column is placed. This column can be heated uniformly to more than 400°C, if necessary. The enclosure must have low thermal inertia, enabling a rapid but controlled temperature rise when a temperature gradient is included in the analysis (gradient can reach 130–140°C/min. with excellent stabilization at 0.05°C). By installation of a cryogenic valve fed with nitrogen or carbon dioxide in the liquid state, the oven can be very quickly regulated at low temperature. This valve is essential when we work with an autosampler and a temperature gradient, as temperature cycles must succeed each other at a few minutes’ interval between two injections.